Asymmetric Sonogashira C(sp3)–C(sp) bond coupling enabled by a copper(i) complex of a new guanidine-hybrid ligand

Abstract

A type of new chiral nitrogen-donor hybrid ligand bearing acyclic guanidine, amide, and pyridine subunits was rationalized for Cu(I)-catalyzed asymmetric Sonogashira C(sp³)–C(sp) cross-coupling. In connection with CuI, the reaction between diverse racemic secondary alkyl bromides and terminal alkynes proceeded smoothly to afford the coupling products in good outcomes (up to 96% yield and 95.5 : 4.5 er). The assembly of guanidine and pyridine with an amide linker is crucial for adjusting the redox ability of copper species, enabling efficient radical generation from alkyl bromides. The chiral ligands are easily accessible and readily modifiable using various amino acids and 2-picolylamine derivatives. This protocol provides new tools for copper salt-involved asymmetric radical transformations.